The prior art discloses CNC-controlled machine tools comprising at least 5 axes and enabling the free movement of a tool in 5 degrees of freedom through the space to remove material from the workpiece. The 5 degree of freedom movements here comprise the at least three spatial degrees of freedom (conventionally three orthogonally controllable spatial degrees of freedom, in particular referred to as the x-axis, y-axis and z-axis) which can be controlled by at least three linear axes, and at least two angular or rotational degrees of freedom which enable any tool orientation. The angular and rotational degrees of freedom can here be controlled by two or more rotational axes of the machine tool.
Today's CNC machine tools having at least 5 axes enable the simultaneous control of the 5 degrees of freedom so as to make possible particularly complex and efficient tool paths relative to a clamped workpiece. In addition, the prior art discloses CNC machine tools having 6 axes on which 3 linear axes and 3 rotational axes can simultaneously be controlled. CNC machine tools having more than 6 axes are also possible.
The above described CNC machine tools are universally used in tool construction to produce finished parts having a complex geometry efficiently and precisely by means of machining. In mechanical engineering, in particular in shipbuilding, for example, in the environmental technology (e.g. in the case of wind power plants), in aviation and in machine tool manufacture, it may also be necessary to provide transmissions having the most different outputs, for which gear wheels, in particular spur gears and bevel gears, have to be produced according to different demands made on surface finish, tooth contact pattern and running characteristics and/or rolling characteristics. Here, it is often not absolutely necessary to obtain a large number of items but it is rather imperative to achieve a high flexibility with respect to the broad range of types, in particular with respect to individual geometries comprising complex flank geometries and complex tooth flank geometries.
For the production of finished parts having a gearing, in particular gear wheels, such as spur gears or bevel gears, and also toothed racks, the prior art discloses special machine tools which are equipped with special tools to produce tooth profiles of gear wheels, such as spur gears or bevel gears, in different embodiments. As special machines for the production of a gearing of gear wheels or toothed racks, the prior art particularly discloses hobbing machines suited to provide a workpiece with a gearing in a hobbing process by means of hobbing tools.
Such special machines, in particular the above described hobbing machines, are cost-intensive as regards purchase and maintenance and the manufacture of individual flank profiles is limited by the shape of the special tools, e.g. the special shape of the cutter of the hobbing tools of hobbing machines, which already predefines an achievable or producible tooth and flank geometry. Moreover, the manufacture of individual flank profiles on the above described special machines is limited by the restricted degrees of freedom in a possible relative movement between workpiece and tool.
To achieve a high surface finish it is also optionally necessary to remachine or finish the workpieces after the machining operation on the above described special machines, e.g. on additional special machines.
In order to solve the problems of the above mentioned special machines, in particular the hobbing machines, for the production of gear wheels, in particular spur gears or bevel gears, or toothed racks, it is useful to produce such gear wheels, in particular spur gears or bevel gears, on a CNC-controlled machine tool comprising at least 5 axes.
This enables the use of standard tools for the production of these finished parts, the most complex geometries, in particular the most complex flank profiles, which extend beyond the possibilities on special machines known to date being enabled with gear wheels, such as spur gears or bevel gears, by the high flexibility and the broad field of application of a machine tool controllable in at least 5 degrees of freedom.
A process for machining a workpiece for the production of a predetermined gear wheel on a machine tool comprising at least 5 axes is described in the article “Auf einfachem Weg zu guten Zähnen—Zahnräder mit holier Qualität auf Standardmaschinen fräsen” [the easy way to good teeth—mill high-quality gear wheels on standard machines] by Hans-Peter Schossig (published in the journal Werkstatt unci Betrieb, Carl Hanser Verlag, Munich, 2007 edition, No. 4/28, pages 28-32, ISSN 0043-2792).
This above mentioned article describes a process for the production of gear wheels by means of a machine tool comprising 5 axes, in particular in the test run for the production of a bevel gear pairing having a surface finish of gearing quality 6 according to DIN 3965. In the described process, all necessary parameters of the gearing according to DIN standard are initially inputted. This corresponds to fundamental geometry parameters of the finished part geometry of the finished part. For this purpose, it is e.g. also possible to input quantitative data on a desired tooth contact pattern in the case of a predetermined or required tooth shape or further data on a desired convexity or further data concerning a curvature in individual areas or over the entire tooth flank or the entire tooth flank profile. Here, prior to the actual machining operation a target geometry of the gearing is given or determined, in particular a desired tooth flank geometry and/or desired tooth gap geometry, for example.
These fundamental geometry parameters are typed in a computer terminal and then a mathematical description of the desired tooth geometry is generated in the computer by mathematical and/or numerical calculations. By means of a CAD/CAM system, an NC program is generated based on the computer result according to which the 5-axis machine tool can produce the desired finished part using standard tools, in particular e.g. a known end mill. A similar process is also shown in WO 2008/133517 A1, for example.
The above described production processes for finished parts having such gearings on a machine tool comprising at least 5 axes, in particular for the production of gear wheels, here involve the problem that after the machining operation on the machine tool it has to be determined whether the predetermined gearing quality, a desired surface finish, a desired tooth flank geometry, a desired tooth gap geometry, in particular the desired tooth flank profile, and/or further predetermined quality requirements have been achieved or could be complied with in the machining operation performed on a CNC machine tool.
To this end, it is optionally necessary to unclamp the machined workpiece after the machining operation on the CNC machine tool from a clamping means of the machine tool and to subsequently check in a test system whether the above mentioned, given quality requirements have been achieved or complied with. If it turns out here that a desired target gearing geometry could not be achieved in the machining operation performed on a CNC machine tool, the workpiece must optionally be remachined or finished on another machine or be machined again after reclamping it in the CNC machine tool.